Method, apparatus, and computer program product for anonymizing trajectories

ABSTRACT

A method, apparatus, and computer program product are provided for anonymizing the trajectory of a vehicle. Methods may include: receiving a sequence of probe data points defining a trajectory; for a subset of the sequence of probe data points defining the trajectory beginning at an origin: updating a counter value at each probe data point, where the counter value is updated based, at least in part, on properties of a number of road links emanating from each junction through which the trajectory passed to reach a location associated with the respective probe data point; in response to the counter value satisfying a predetermined value after an update relative to a given probe data point, removing probe data points before the given probe data point in the sequence of probe data points to obtain origin-obscured probe data points; and creating a cropped trajectory including the origin-obscured probe data points.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 63/054,950, Filed on Jul. 22, 2020, the contents of which are herebyincorporated by reference in their entirety.

TECHNOLOGICAL FIELD

An example embodiment of the present disclosure relates to anonymizingtrajectories of mobile devices, and more particularly, to pruning orcropping of a beginning and an end of a trajectory between an origin anda destination to remove identifiable information from the trajectory.

BACKGROUND

Service providers and device manufacturers (e.g., wireless, cellular,navigation, etc.) are continually challenged to deliver value andconvenience to consumers by providing compelling and useful services.Location-based services have been developed to provide users with usefuland relevant information regarding route planning and to facilitateroute guidance along the way. Substantially static data regardingroadways is used in conjunction with dynamic data, such as traffic,construction, and incident information to provide accurate and timelyinformation to a driver to help route planning and decision making.

Data received from infrastructure monitoring systems and crowd-sourceddata has become ubiquitous and may be available for facilitating routeguidance and navigation system information. However, this data can bemined to provide various other services to users and to grow theavailability of location-based services. The provision of location-basedservices is dependent upon understanding the location of a userrequesting the services. Maintaining anonymity while also being able toaccess location-based services is a challenge.

BRIEF SUMMARY

A method, apparatus, and computer program product are provided inaccordance with an example embodiment described herein for anonymizingtrajectories of mobile devices, and more particularly, to pruning orcropping of a beginning and an end of a trajectory between an origin anda destination to remove identifiable information from the trajectory.According to an example embodiment, an apparatus is provided includingat least one processor and at least one memory including computerprogram code, the at least one memory and computer program codeconfigured to, with the processor, cause the apparatus to at least:receive a sequence of probe data points defining a trajectory; for asubset of the sequence of probe data points defining the trajectorybeginning at the origin: update a counter value at each probe datapoint, where the counter value is updated based, at least in part, onproperties of a number of road links emanating from each junctionthrough which the trajectory passed to reach a location associated withthe respective probe data point; and in response to the counter valuesatisfying a predetermined value after an update relative to a givenprobe data point, remove probe data points before the given probe datapoint in the sequence of probe data points to obtain origin-obscuredprobe data points; and create a cropped trajectory including theorigin-obscured probe data points.

According to some embodiments, the predetermined value includes a randomnumber within a predefined range. The apparatus of some embodiments maybe caused to provide the cropped trajectory to a location-based serviceprovider. The properties of the number of road links emanating from eachjunction is identified based on an accessibility map of a road networkthrough which the trajectory passes. The accessibility map may includeinformation defining possible ways of entering and leaving junctions ofthe road networks factoring in properties of the map including anallowable direction of travel in each road link. The counter value maybe updated based, at least in part, on a score for each junction throughwhich the trajectory passed to reach the location associated with therespective probe data point, where the score is obtained from anaccessibility map.

According to an example embodiment, the subset of the sequence of probedata points includes an origin sequence, where the apparatus is furthercaused to: receive an indication of a probe data point defining an endof the trajectory; and for a destination sequence of probe data pointsbeginning with the probe data point defining the end of the trajectory:update a second counter value, where the second counter value is updatedbased, at least in part, on a number of road links emanating from eachjunction through which the trajectory passes as the trajectory is tracedin reverse to reach a location associated with the respective probe datapoint along the trajectory; and in response the second counter valueupdated for a given probe data point of the ending sequence of probedata points satisfying a predetermined value, remove probe data pointsafter the given probe data point in the ending sequence of probe datapoints from the origin-obscured probe data points to obtainorigin-obscured and destination-obscured probe data points, wherecausing the apparatus to create a cropped trajectory includes causingthe apparatus to create a cropped trajectory from the origin-obscuredand destination-obscured probe data points. Causing the apparatus ofsome embodiments to create a cropped trajectory includes causing theapparatus to: remove any information from the cropped trajectoryidentifying an entrance to a junction at the beginning of the croppedtrajectory; and remove any information from the cropped trajectoryidentifying an exit from a junction at the end of the croppedtrajectory.

Embodiments provided herein include a computer program product having atleast one non-transitory computer-readable storage medium havingcomputer-executable program code portions stored therein, thecomputer-executable program code portions including program codeinstructions configured to: receive a sequence of probe data pointsdefining a trajectory; for a subset of the sequence of probe data pointsdefining the trajectory beginning at an origin: update a counter valueat each probe data point, where the counter value is updated based, atleast in part, on properties of a number of road links emanating fromeach junction through which the trajectory passed to reach a locationassociated with the respective probe data point; in response to thecounter value satisfying a predetermined value after an update relativeto a given probe data point, remove probe data points before the givenprobe data point in the sequence of probe data points to obtainorigin-obscured probe data points; and create a cropped trajectoryincluding the origin-obscured probe data points.

According to an example embodiment, the predetermined value includes arandom number within a predefined range. Embodiments may include programcode instructions to provide the cropped trajectory to a location-basedservice provider. The properties of the number of road links emanatingfrom each junction may be identified based on an accessibility map of aroad network through which the trajectory passes. The accessibility mapmay include information defining possible ways of entering and leavingjunctions of the road networks factoring in properties of the mapincluding an allowable direction of travel in each road link. Thecounter value may be updated based, at least in part, on a score foreach junction through which the trajectory passed to reach the locationassociated with the respective probe data point, where the score isobtained from an accessibility map.

According to an example embodiment, the subset of the sequence of probedata points includes an origin sequence, where the computer programproduct further includes program code instructions to: receive anindication of a probe data point defining an end of the trajectory; fora destination sequence of the probe data points beginning with the probedata point defining the end of the trajectory: update a second countervalue, where the second counter value is updated based, at least inpart, on a number of road links emanating from each junction throughwhich the trajectory passes as the trajectory is traced in reverse toreach a location associated with the respective probe data point alongthe trajectory; and in response to the second counter value updated fora given probe data point of the ending sequence of probe data pointssatisfying a predetermined value, remove probe data points after thegiven probe data point in the ending sequence of probe data points fromthe origin-obscured probe data points to obtain origin-obscured anddestination-obscured probe data points, where the program codeinstructions to create a cropped trajectory includes program codeinstructions to create a cropped trajectory from the origin-obscured anddestination-obscured probe data points. The program code instructions tocreate a cropped trajectory may further include program codeinstructions to: remove any information from the cropped trajectoryidentifying an entrance to a junction at the beginning of the croppedtrajectory; and remove any information from the cropped trajectoryidentifying an exit from a junction at the end of the croppedtrajectory.

Embodiments provided herein include a method including: receiving asequence of probe data points defining a trajectory; for a subset of thesequence of probe data points defining the trajectory beginning at anorigin: updating a counter value at each probe data point, where thecounter value is updated based, at least in part, on properties of anumber of road links emanating from each junction through which thetrajectory passed to reach a location associated with the respectiveprobe data point; in response to the counter value satisfying apredetermined value after an update relative to a given probe datapoint, removing probe data points before the given probe data point inthe sequence of probe data points to obtain origin-obscured probe datapoints; and creating a cropped trajectory including the origin-obscuredprobe data points. The predetermined value may include a random numberwithin a predefined range. Embodiments may include providing the croppedtrajectory to a location-based service provider. The properties of thenumber of road links emanating from each junction may be identifiedbased on an accessibility map of a road network through which thetrajectory passes.

Embodiments provided herein include an apparatus including: means forreceiving a sequence of probe data points defining a trajectory; for asubset of the sequence of probe data points defining the trajectorybeginning at an origin: means for updating a counter value at each probedata point, where the counter value is updated based, at least in part,on properties of a number of road links emanating from each junctionthrough which the trajectory passed to reach a location associated withthe respective probe data point; in response to the counter valuesatisfying a predetermined value after an update relative to a givenprobe data point, means for removing probe data points before the givenprobe data point in the sequence of probe data points to obtainorigin-obscured probe data points; and means for creating a croppedtrajectory including the origin-obscured probe data points. Thepredetermined value may include a random number within a predefinedrange. Embodiments may include means for providing the croppedtrajectory to a location-based service provider. The properties of thenumber of road links emanating from each junction may be identifiedbased on an accessibility map of a road network through which thetrajectory passes.

Embodiments provided herein include an apparatus having at least oneprocessor and at least one memory including computer program code, theat least one memory and computer program code configured to, with theprocessor, cause the apparatus to at least: receive probe dataassociated with a vehicle, where the probe data includes probe datapoints, each probe data point including a location and a timestamp;determine a trajectory based on the probe data beginning at an origin;in response to a counter value failing to satisfy a predetermined value:advance to a next probe data point; associate the next probe data pointto a map element; and in response to the map element corresponding to ajunction, update the counter value based, at least in part, on a numberof road links intersecting at the junction; in response to the countervalue satisfying the predetermined value: modify the trajectory to beginwith a probe data point associated with a map element corresponding to ajunction having caused the counter to satisfy the predetermined value.The predetermined value may include a random number within a predefinedrange.

Embodiments may include causing the apparatus to remove from thetrajectory any information identifying an entrance to a junction at abeginning of the modified trajectory. The apparatus of some embodimentsis caused to: estimate a destination of the trajectory; identify aboundary around the estimated destination of the trajectory; and end themodified trajectory at alas probe data point received outside of theboundary. Causing the apparatus to provide the modified trajectory to aservice provider may include causing the apparatus to: provide themodified trajectory to a service provider with a time delay from thetime at which the probe data was received; and cease to provide themodified trajectory in response to determining that the vehicle hasreached a location proximate the destination. The number of road linksintersecting at each junction may be identified based on anaccessibility map of a road network through which the trajectory passes.The accessibility map may include information defining possible ways ofentering and leaving junctions of the road network factoring inproperties of the map including an allowable direction of travel in eachroad link.

Embodiments provided herein include a computer program product includingat least one non-transitory computer-readable storage medium havingcomputer-executable program code portions stored therein. Thecomputer-executable program code portions including program codeinstructions configured to: receive probe data associated with avehicle, where the probe data includes probe data points, each probedata point including a location and a timestamp; determine a trajectorybased on the probe data beginning at an origin; in response to a countervalue failing to satisfy a predetermined value: advance to a next probedata point; associate the next probe data point to a map element; and inresponse to the map element corresponding to a junction, update thecounter value based, at least in part, on a number of road linksintersecting at the junction; in response to the counter valuesatisfying the predetermined value: modify the trajectory to begin witha probe data point associated with a map element corresponding to ajunction having caused the counter to satisfy the predetermined value.The predetermined value may include a random number within a predefinedrange.

According to an example embodiment, the computer program productincludes program code instructions to remove from the trajectory anyinformation identifying an entrance to a junction at a beginning of themodified trajectory. Embodiments may include program code instructionsto: estimate a destination of the trajectory; identify a boundary aroundthe estimated destination of the trajectory; and end the modifiedtrajectory at a last probe data point received outside of the boundary.The program code instructions to provide the modified trajectory to aservice provider may include program code instructions to: provide themodified trajectory to a service provider with a time delay from thetime at which the probe data was received; and cease to provide themodified trajectory in response to determining that the vehicle hasreached a location proximate the destination. The number of road linksintersecting at each junction may be identified based on anaccessibility map of a road network through which the trajectory passes.The accessibility map may include information defining possible ways ofentering and leaving junctions of the road networks factoring inproperties of the map including an allowable direction of travel in eachroad link.

Embodiments provided herein include a method including: receiving probedata associated with a vehicle, where the probe data includes probe datapoints, each probe data point including a location and a timestamp;determine a trajectory based on the probe data beginning at an origin;in response to a counter value failing to satisfy a predetermined value:advancing to a next probe data point; associating the next probe datapoint to a map element; and in response to the map element correspondingto a junction, updating the counter value based, at least in part, on anumber of road links intersecting at the junction; in response to thecounter value satisfying the predetermined value: modifying thetrajectory to begin with a probe data point associated with a mapelement corresponding to a junction having caused the counter to satisfythe predetermined value. The predetermined value may include a randomnumber within a predefined range.

Methods may include removing from the trajectory any informationidentifying an entrance to a junction at a beginning of the modifiedtrajectory. Methods may include: estimating a destination of thetrajectory; identifying a boundary around the estimated destination ofthe trajectory; and ending the modified trajectory at a last probe datapoint received outside of the boundary. Providing the modifiedtrajectory to a service provider may include: providing the modifiedtrajectory to a service provider with a time delay from the time atwhich the probe data was received; and ceasing to provide the modifiedtrajectory in response to determining that the vehicle has reached alocation proximate the destination. The number of road linksintersecting at each junction may be identified based on anaccessibility map of a road network through which the trajectory passes.

Embodiments provided herein include an apparatus including: means forreceiving probe data associated with a vehicle, where the probe dataincludes probe data points, each probe data point including a locationand a timestamp; means for determine a trajectory based on the probedata beginning at an origin; in response to a counter value failing tosatisfy a predetermined value: means for advancing to a next probe datapoint; means for associating the next probe data point to a map element;and in response to the map element corresponding to a junction, meansfor updating the counter value based, at least in part, on a number ofroad links intersecting at the junction; in response to the countervalue satisfying the predetermined value: means for modifying thetrajectory to begin with a probe data point associated with a mapelement corresponding to a junction having caused the counter to satisfythe predetermined value. The predetermined value may include a randomnumber within a predefined range.

The apparatus of example embodiments may include means for removing fromthe trajectory any information identifying an entrance to a junction ata beginning of the modified trajectory. An example apparatus mayinclude: means for estimating a destination of the trajectory; means foridentifying a boundary around the estimated destination of thetrajectory; and means for ending the modified trajectory at a last probedata point received outside of the boundary. The means for providing themodified trajectory to a service provider may include: means forproviding the modified trajectory to a service provider with a timedelay from the time at which the probe data was received; and means forceasing to provide the modified trajectory in response to determiningthat the vehicle has reached a location proximate the destination. Thenumber of road links intersecting at each junction may be identifiedbased on an accessibility map of a road network through which thetrajectory passes.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described example embodiments of the disclosure in generalterms, reference will now be made to the accompanying drawings, whichare not necessarily drawn to scale, and wherein:

FIG. 1 illustrates a communications diagram in accordance with anexample embodiment of the present disclosure;

FIG. 2 is a block diagram of an apparatus that may be specificallyconfigured for anonymizing trajectories generated from probe data inaccordance with an example embodiment of the present invention;

FIG. 3 is a diagram of a trajectory passing through junctions andincreasing a counter according to an example embodiment of the presentdisclosure;

FIG. 4 illustrates an algorithm for determining where to crop atrajectory to maintain privacy according to an example embodiment of thepresent disclosure;

FIG. 5 is another diagram of a trajectory passing through junctions andincreasing a counter according to an example embodiment of the presentdisclosure;

FIG. 6 is a flowchart of a method for determining where to crop atrajectory to maintain privacy according to an example embodiment of thepresent disclosure; and

FIG. 7 is a flowchart of a method for anonymizing trajectories of mobiledevices according to an example embodiment of the present disclosure.

DETAILED DESCRIPTION

Some embodiments of the present disclosure will now be described morefully hereinafter with reference to the accompanying drawings, in whichsome, but not all, embodiments of the invention are shown. Indeed,various embodiments of the invention may be embodied in many differentforms and should not be construed as limited to the embodiments setforth herein; rather, these embodiments are provided so that thisdisclosure will satisfy applicable legal requirements. Like referencenumerals refer to like elements throughout. As used herein, the terms“data,” “content,” “information,” and similar terms may be usedinterchangeably to refer to data capable of being transmitted, receivedand/or stored in accordance with embodiments of the present invention.Thus, use of any such terms should not be taken to limit the spirit andscope of embodiments of the present disclosure.

A method, apparatus, and computer program product are provided herein inaccordance with an example embodiment for anonymizing trajectories ofmobile devices, and more particularly, to pruning or cropping of abeginning and an end of a trajectory between an origin and a destinationto remove identifiable information from the trajectory. Location-basedservices are useful to a variety of consumers who may employlocation-based services for a wide range of activities. Services such asthe identification of traffic location and density, providinginformation regarding goods and services available in a specificlocation, and identifying a target group of consumers in a particularlocation or who travel along a particular path, are among many otherlocation-based services. While location-based services are desirable forboth consumers and for service providers, consumers are often concernedwith the amount of information shared about their routines andactivities. Thus, while consumers and service providers want to engagewith location-based services, consumers generally desire to maintainsome degree of privacy. Embodiments described herein provide a method,apparatus, and computer program product through which locationinformation and more specifically, trajectory information can begathered and shared in a manner that anonymizes the source of theinformation and makes unmasking of the source difficult. Embodiments useonly a portion of a trajectory of a user, where a trajectory is a pathof a user between an origin and a destination, often identified by anumber of time-stamped location points. Embodiments crop a portion atthe beginning of the trajectory to mask the origin of the trajectory,and crop a portion at the end of the trajectory to mask the destinationof the trajectory, thereby rendering it difficult to establish to whomthe trajectory belongs while obtaining useful location-based trajectoryinformation for use with location-based services.

To provide an improved manner of anonymizing trajectories, a system asillustrated in FIG. 1 may be used. FIG. 1 illustrates a communicationdiagram of an example embodiment of a system for implementing exampleembodiments described herein. The illustrated embodiment of FIG. 1includes a map developer system 116, a processing server 102 in datacommunication with an original equipment manufacturer (OEM) 104 and/or ageographic map database, e.g., map database 108 through a network 112,and one or more mobile devices 114. The OEM may be one form of atrajectory source from which a trajectory of a probe or mobile device isreceived. The trajectory source may optionally include third partyservice providers or app developers, for example. The mobile device 114may be associated, coupled, or otherwise integrated with a vehicle, suchas in a vehicle's head unit, infotainment unit, or an advanced driverassistance system (ADAS), for example. Additional, different, or fewercomponents may be provided. For example, many mobile devices 114 mayconnect with the network 112. The map developer 116 may include computersystems and network of a system operator. The processing server 102 mayinclude the map database 108, such as a remote map server. The networkmay be wired, wireless, or any combination of wired and wirelesscommunication networks, such as cellular, Wi-Fi, internet, local areanetworks, or the like.

The OEM 104 may include a server and a database configured to receiveprobe data from vehicles or devices corresponding to the OEM. Forexample, if the OEM is a brand of automobile, each of thatmanufacturer's automobiles (e.g., mobile device 114) may provide probedata to the OEM 104 for processing. That probe data may be encryptedwith a proprietary encryption or encryption that is unique to the OEM.The OEM may be the manufacturer or service provider for a brand ofvehicle or a device. For example, a mobile device carried by a user(e.g., driver or occupant) of a vehicle may be of a particular brand orservice (e.g., mobile provider), where the OEM may correspond to theparticular brand or service. The OEM may optionally include a serviceprovider to which a subscriber subscribes, where the mobile device 114may be such a subscriber. While depicted as an OEM 104 in FIG. 1, otherentities may function in the same manner described herein with respectto the OEM. For example, independent location-based service providers orother entities may participate and contribute in the same manner asdescribed herein with respect to an OEM. As such, the OEM 104illustrated in FIG. 1 is not limited to original equipmentmanufacturers, but may be any entity participating as described hereinwith respect to the OEMs.

The OEM 104 may be configured to access the map database 108 via theprocessing server 102 through, for example, a mapping application, suchthat the user equipment may provide navigational assistance to a useramong other services provided through access to the map developer 116.According to some embodiments, the map developer 116 may function as theOEM, such as when the map developer is a service provider to OEMs toprovide map services to vehicles from that OEM. In such an embodiment,the map developer 116 may or may not be the recipient of vehicle probedata from the vehicles of that manufacturer. Similarly, the mapdeveloper 116 may provide services to mobile devices, such as a mapservices provider that may be implemented on a mobile device, such as ina mapping application. According to such an embodiment, the mapdeveloper 116 may function as the OEM as the map developer receives theprobe data from the mobile devices of users as they travel along a roadnetwork.

The map database 108 may include node data, road segment data or linkdata, point of interest (POI) data, or the like. The map database 108may also include cartographic data, routing data, and/or maneuveringdata. According to some example embodiments, the road segment datarecords may be links or segments representing roads, streets, or paths,as may be used in calculating a route or recorded route information fordetermination of one or more personalized routes. The node data may beend points corresponding to the respective links or segments of roadsegment data. The road link data and the node data may represent a roadnetwork, such as used by vehicles, cars, trucks, buses, motorcycles,and/or other entities. Optionally, the map database 108 may contain pathsegment and node data records or other data that may representpedestrian paths or areas in addition to or instead of the vehicle roadrecord data, for example. The road/link segments and nodes can beassociated with attributes, such as geographic coordinates, streetnames, address ranges, speed limits, turn restrictions at intersections,and other navigation related attributes, as well as POIs, such asfueling stations, hotels, restaurants, museums, stadiums, offices, autorepair shops, buildings, stores, parks, etc. The map database 108 caninclude data about the POIs and their respective locations in the POIrecords. The map database 108 may include data about places, such ascities, towns, or other communities, and other geographic features suchas bodies of water, mountain ranges, etc. Such place or feature data canbe part of the POI data or can be associated with POIs or POI datarecords (such as a data point used for displaying or representing aposition of a city). In addition, the map database 108 can include eventdata (e.g., traffic incidents, construction activities, scheduledevents, unscheduled events, etc.) associated with the POI data recordsor other records of the map database 108.

The map database 108 may be maintained by a content provider e.g., a mapdeveloper. By way of example, the map developer can collect geographicdata to generate and enhance the map database 108. There can bedifferent ways used by the map developer to collect data. These ways caninclude obtaining data from other sources, such as municipalities orrespective geographic authorities. In addition, the map developer canemploy field personnel to travel by vehicle along roads throughout thegeographic region to observe features and/or record information aboutthem, for example. Also, remote sensing, such as aerial or satellitephotography, can be used to generate map geometries directly or throughmachine learning as described herein.

The map database 108 may be a master map database stored in a formatthat facilitates updating, maintenance, and development. For example,the master map database or data in the master map database can be in anOracle spatial format or other spatial format, such as for developmentor production purposes. The Oracle spatial format ordevelopment/production database can be compiled into a delivery format,such as a geographic data files (GDF) format. The data in the productionand/or delivery formats can be compiled or further compiled to formgeographic database products or databases, which can be used in end usernavigation devices or systems.

For example, geographic data may be compiled (such as into a platformspecification format (PSF) format) to organize and/or configure the datafor performing navigation-related functions and/or services, such asroute calculation, route guidance, map display, speed calculation,distance and travel time functions, and other functions, by a navigationdevice, such as by mobile device 114, for example. Further, data may becompiled relating to the existence of parking and parking spaceavailability along different road segments of the map database, where aparking availability estimation may be generated in dependence of timeof day, day of week, season of the year, special events, etc. Park-inand park-out events, may be established based on the assessment ofwhether a vehicle is performing a parking maneuver followed by a stop inmovement of the probe (park-in) or a vehicle is performing a parkingmaneuver followed by continued movement of the probe (park-out), and therelative movement of vehicles performing park-in to performing park-outmaneuvers can be used to estimate parking availability. Further, thisdata can be compiled for temporal clustering of epochs to estimatefuture parking availability. The navigation-related functions cancorrespond to vehicle navigation, pedestrian navigation, or other typesof navigation. While example embodiments described herein generallyrelate to vehicular travel and parking along roads, example embodimentsmay be implemented for bicycle travel along bike paths and bikerack/parking availability, boat travel along maritime navigationalroutes including dock or boat slip availability, etc. The compilation toproduce the end user databases can be performed by a party or entityseparate from the map developer. For example, a customer of the mapdeveloper, such as a navigation device developer or other end userdevice developer, can perform compilation on a received map database ina delivery format to produce one or more compiled navigation databases.

As mentioned above, the server side map database 108 may be a mastergeographic database, but in alternate embodiments, a client side mapdatabase 108 may represent a compiled navigation database that may beused in or with end user devices (e.g., mobile device 114) to providenavigation and/or map-related functions. For example, the map database108 may be used with the mobile device 114 to provide an end user withnavigation features. In such a case, the map database 108 can bedownloaded or stored on the end user device (mobile device 114) whichcan access the map database 108 through a wireless or wired connection,such as via a processing server 102 and/or the network 112, for example.

In one embodiment, the mobile device 114 can be an in-vehicle navigationsystem, such as an ADAS, a personal navigation device (PND), a portablenavigation device, a cellular telephone, a smart phone, a personaldigital assistant (PDA), a watch, a camera, a computer, and/or otherdevice that can perform navigation-related functions, such as digitalrouting and map display. An end user can use the mobile device 114 fornavigation and map functions such as guidance and map display, forexample, and for determination of one or more personalized routes orroute segments based on one or more calculated and recorded routes,according to some example embodiments.

An ADAS may be used to improve the comfort, efficiency, safety, andoverall satisfaction of driving. Examples of such advanced driverassistance systems include semi-autonomous driver assistance featuressuch as adaptive headlight aiming, adaptive cruise control, lanedeparture warning and control, curve warning, speed limit notification,hazard warning, predictive cruise control, adaptive shift control, amongothers. Other examples of an ADAS may include provisions for fullyautonomous control of a vehicle to drive the vehicle along a roadnetwork without requiring input from a driver. Some of these advanceddriver assistance systems use a variety of sensor mechanisms in thevehicle to determine the current state of the vehicle and the currentstate of the roadway ahead of the vehicle. These sensor mechanisms mayinclude radar, infrared, ultrasonic, and vision-oriented sensors such asimage sensors and light distancing and ranging (LiDAR) sensors.

Some advanced driver assistance systems may employ digital map data.Such systems may be referred to as map-enhanced ADAS. The digital mapdata can be used in advanced driver assistance systems to provideinformation about the road network, road geometry, road conditions, andother information associated with the road and environment around thevehicle. Unlike some sensors, the digital map data is not affected bythe environmental conditions such as fog, rain, or snow. Additionally,the digital map data can provide useful information that cannot reliablybe provided by sensors, such as curvature, grade, bank, speed limitsthat are not indicated by signage, lane restrictions, and so on.Further, digital map data can provide a predictive capability wellbeyond the driver's vision to determine the road ahead of the vehicle,around corners, over hills, or beyond obstructions.

Accordingly, the digital map data can be a useful and sometimesnecessary addition for some advanced driving assistance systems. In theexample embodiment of a fully-autonomous vehicle, the ADAS uses thedigital map data to determine a path along the road network to drive,such that accurate representations of the road are necessary, such asaccurate representations of intersections and turn maneuvers therethrough.

The processing server 102 may receive probe data, directly orindirectly, from a mobile device 114, such as when the map developer isfunctioning as the OEM 104. Optionally, the map developer 116 mayreceive probe data indirectly from the mobile device 114, such as whenthe mobile device 114 provides probe data to the OEM 104, and the OEMprovides certain elements of the probe data to the map developer 116.The OEM 104 may anonymize the probe data or otherwise process the probedata to maintain privacy of a user of the mobile device 114 beforeproviding the data to the map developer 116. The mobile device 114 mayinclude one or more detectors or sensors as a positioning system builtor embedded into or within the interior of the mobile device 114.Alternatively, the mobile device 114 uses communications signals forposition determination. The mobile device 114 may receive location datafrom a positioning system, such as a global positioning system (GPS),cellular tower location methods, access point communicationfingerprinting, or the like. The server 102, either directly orindirectly, may receive sensor data configured to describe a position ofa mobile device, or a controller of the mobile device 114 may receivethe sensor data from the positioning system of the mobile device 114.The mobile device 114 may also include a system for tracking mobiledevice movement, such as rotation, velocity, or acceleration. Movementinformation may also be determined using the positioning system. Themobile device 114 may use the detectors and sensors to provide dataindicating a location of a vehicle. This vehicle data, also referred toherein as “probe data”, may be collected by any device capable ofdetermining the necessary information, and providing the necessaryinformation to a remote entity. The mobile device 114 is one example ofa device that can function as a probe to collect probe data of avehicle.

More specifically, probe data (e.g., collected by mobile device 114) maybe representative of the location of a vehicle at a respective point intime and may be collected while a vehicle is traveling along a route.According to the example embodiment described below with the probe databeing from motorized vehicles traveling along roadways, the probe datamay include, without limitation, location data, (e.g. a latitudinal,longitudinal position, and/or height, GPS coordinates, proximityreadings associated with a radio frequency identification (RFID) tag, orthe like), rate of travel, (e.g. speed), direction of travel, (e.g.heading, cardinal direction, or the like), device identifier, (e.g.vehicle identifier, user identifier, or the like), a time stampassociated with the data collection, or the like. The mobile device 114,may be any device capable of collecting the aforementioned probe data.Some examples of the mobile device 114 may include specialized vehiclemapping equipment, navigational systems, mobile devices, such as phonesor personal data assistants, or the like.

An example embodiment of a processing server 102 and/or an OEM 104 maybe embodied in an apparatus as illustrated in FIG. 2. The apparatus,such as that shown in FIG. 2, may be specifically configured inaccordance with an example embodiment of the present disclosure fordetermining parking availability along road segments within regions of amap. Parking availability is described herein as whether or not parkingspaces may be available (i.e., are not currently occupied). Theapparatus may include or otherwise be in communication with a processor202, a memory device 204, a communication interface 206, and a userinterface 208. In some embodiments, the processor (and/or co-processorsor any other processing circuitry assisting or otherwise associated withthe processor) may be in communication with the memory device via a busfor passing information among components of the apparatus. The memorydevice may be non-transitory and may include, for example, one or morevolatile and/or non-volatile memories. In other words, for example, thememory device may be an electronic storage device (for example, acomputer readable storage medium) comprising gates configured to storedata (for example, bits) that may be retrievable by a machine (forexample, a computing device like the processor 202). The memory devicemay be configured to store information, data, content, applications,instructions, or the like, for enabling the apparatus to carry outvarious functions in accordance with an example embodiment of thepresent invention. For example, the memory device could be configured tobuffer input data for processing by the processor. Additionally oralternatively, the memory device could be configured to storeinstructions for execution by the processor.

The processor 202 may be embodied in a number of different ways. Forexample, the processor may be embodied as one or more of varioushardware processing means such as a coprocessor, a microprocessor, acontroller, a digital signal processor (DSP), a processing element withor without an accompanying DSP, or various other processing circuitryincluding integrated circuits such as, for example, an ASIC (applicationspecific integrated circuit), an FPGA (field programmable gate array), amicrocontroller unit (MCU), a hardware accelerator, a special-purposecomputer chip, or the like. As such, in some embodiments, the processormay include one or more processing cores configured to performindependently. A multi-core processor may enable multiprocessing withina single physical package. Additionally or alternatively, the processormay include one or more processors configured in tandem via the bus toenable independent execution of instructions, pipelining and/ormultithreading.

In an example embodiment, the processor 202 may be configured to executeinstructions stored in the memory device 204 or otherwise accessible tothe processor. Alternatively or additionally, the processor may beconfigured to execute hard coded functionality. As such, whetherconfigured by hardware or software methods, or by a combination thereof,the processor may represent an entity (for example, physically embodiedin circuitry) capable of performing operations according to anembodiment of the present invention while configured accordingly. Thus,for example, when the processor is embodied as an ASIC, FPGA or thelike, the processor may be specifically configured hardware forconducting the operations described herein. Alternatively, as anotherexample, when the processor is embodied as an executor of softwareinstructions, the instructions may specifically configure the processorto perform the algorithms and/or operations described herein when theinstructions are executed. However, in some cases, the processor may bea processor specific device (for example, a mobile terminal or a fixedcomputing device) configured to employ an embodiment of the presentinvention by further configuration of the processor by instructions forperforming the algorithms and/or operations described herein. Theprocessor may include, among other things, a clock, an arithmetic logicunit (ALU) and logic gates configured to support operation of theprocessor.

The apparatus 200 of an example embodiment may also include acommunication interface 206 that may be any means such as a device orcircuitry embodied in either hardware or a combination of hardware andsoftware that is configured to receive and/or transmit data to/from acommunications device in communication with the apparatus, such as tofacilitate communications with one or more user equipment 104 or thelike. In this regard, the communication interface may include, forexample, an antenna (or multiple antennae) and supporting hardwareand/or software for enabling communications with a wirelesscommunication network. Additionally or alternatively, the communicationinterface may include the circuitry for interacting with the antenna(s)to cause transmission of signals via the antenna(s) or to handle receiptof signals received via the antenna(s). In some environments, thecommunication interface may alternatively or also support wiredcommunication. As such, for example, the communication interface mayinclude a communication modem and/or other hardware and/or software forsupporting communication via cable, digital subscriber line (DSL),universal serial bus (USB) or other mechanisms.

The apparatus 200 may also include a user interface 208 that may in turnbe in communication with the processor 202 to provide output to the userand, in some embodiments, to receive an indication of a user input. Assuch, the user interface may include a display and, in some embodiments,may also include a keyboard, a mouse, a joystick, a touch screen, touchareas, soft keys, one or more microphones, a plurality of speakers, orother input/output mechanisms. In one embodiment, the processor maycomprise user interface circuitry configured to control at least somefunctions of one or more user interface elements such as a display and,in some embodiments, a plurality of speakers, a ringer, one or moremicrophones and/or the like. The processor and/or user interfacecircuitry comprising the processor may be configured to control one ormore functions of one or more user interface elements through computerprogram instructions (for example, software and/or firmware) stored on amemory accessible to the processor (for example, memory device 204,and/or the like).

Location-based services (LBS) such as real-time traffic information,fleet management, and navigation among others, are based on the analysisof mobility data that users of such services provide. Mobility data isassociated with a privacy level and accuracy value. An accuracy value isbased on the intrinsic utility of data toward the generation oflocation-based services. The privacy value reflects the sensitiveinformation that mobility data reveals about a user's habits, behaviors,and personal information such as their home and/or work address.

Location-based service providers endeavor to collect as much locationdata as possible to maximize the accuracy of the location-basedservices, while attempting to minimize the associated risks for theprivacy of the users particularly as it relates to the inadvertentdisclosure or misuse of data. To reduce the privacy risk, location-basedservice providers may apply privacy-enhancing algorithms on data.Privacy-enhancing algorithms function by removing or altering featuresof the data that may remove privacy, and this operation typicallyrenders the data less accurate and thus less valuable for thelocation-based service provider.

Embodiments described herein provide privacy to users of location-basedservices by adding uncertainty regarding the origin and destination oftrajectory data of the user. An origin and destination, separately or asa pair, can reveal sensitive locations regarding the user that generatedthe trajectory data, such as a home location and/or a work location, andidentification of an origin, a destination, or both, may render theidentity of the individual user relatively easy to obtain

Trajectory data as described herein is defined as a set of data points,each data point including a location and a timestamp. The location maybe in the form of latitude and longitude, and potentially altitude.Additional information may be associated with a data point, such asspeed, heading, etc. If a trajectory identifier is associated with eachpoint, the trajectory data can be partitioned into a set oftrajectories, each of which identifies the movement of a user over aperiod of time.

Location-based service providers may provide trajectory data tocustomers, such as municipalities interested in traffic optimization,data producers (e.g., drivers who share their trajectory data with theservice provider), or the like. Any trajectory that reveals a user'sbehavioral patterns (e.g., going from A to B) can potentially revealprivacy-sensitive information and locations. Embodiments describedherein mitigate this issue by cropping the trajectories through removalof the initial and final sections of the trajectory in order tointroduce uncertainty about the actual origin and destination of thetrajectory. If a trajectory includes additional sensitive points (e.g.,stopping for a period of time at a location such as a hospital), thesame approach can be applied to sub-trajectories to crop portions of atrajectory around a potentially sensitive location or stopping pointwithin a trajectory. To maximize the utility of the data therebyimproving the location-based services provided by the service provider,embodiments described herein identify a suitable location where to cropthe trajectory based on an analysis of the trajectory.

While the cropping of trajectories can be performed using a constanttemporal threshold (e.g., delete data until 2 minutes after start) orusing a speed threshold (e.g., delete data until after the vehiclereaches a speed of 30 miles-per-hour), such embodiments can performpoorly in many circumstances. For example, a vehicle leaving a parkinglot into a congested road, as a slow-moving vehicle would not get farfrom the parking lot within the temporal threshold. Leaving a parkinglot into a high speed road would reach a speed threshold very quicklyenabling identification of the origin of the trajectory. Leaving a farmin a rural area, where population density is much lower than in a cityand therefore uncertainty about the origin of the trajectory would bemuch lower than desired (e.g., if the road segment where the trajectorystarts leads to only a handful of residential units). Embodimentsdescribed herein solve these issues through a unique method of croppingtrajectories.

Embodiments described herein introduce uncertainty in what is the originand destination of a trajectory while avoiding unnecessary degradationof the data. This is achieved by dynamically choosing where to crop atrajectory based on the context in which the vehicle is located. Giventhat behavior of a vehicle is constrained by the road network,uncertainty will depend on the characteristics of the road network thatthe car is traversing. Algorithms described herein define uncertaintybased on the possible alternative routes that could have been taken.Embodiments include the creation of an accessibility map that counts allpossible ways of entering and leaving every junction and includes ascore that may factor in context of the junction other than the numberof road links emanating from the junction. For example, as will bedetailed further below, a junction may have a higher score or count ifthe junction is in a heavily populated area as the mere indication thata trajectory starts at or near such a junction may not provide asubstantial indication of to whom the trajectory belongs, Similarly, ajunction may have several road links emanating from the junction;however, the junction may be located in a remote area and the likelihoodof identifying an individual beginning a trajectory through thatintersection increases substantially. The algorithms described hereinconsider properties of the map (e.g., the allowed direction of travel ineach road segment) to identify a score for junctions such that the scorecan be used in embodiments described below to update a counter as atrajectory passes through the junction. The accessibility map may alsobe based on other types of information, such as the number ofpoints-of-interest (POIs) proximate an origin or destination, the numberof buildings in an area, the kind/category of buildings in an area, etc.and/or combinations thereof. The accessibility map may then be accessedby the algorithm when cropping trajectories.

A trajectory can be cropped in an on-line fashion or an off-linefashion. Postprocessing of trajectories either on a device or on abackend server (e.g., map services provider 116) is an example ofoff-line cropping, while an on-line cropping example may entail when avehicle (or mobile device 114 thereof) decides when to crop trajectoriesas it proceeds along a path. Embodiments uniquely employ the context ofthe road network while cropping a trajectory thus ensuring privacyprotection across trajectories while maximizing the utility of thetrajectory data.

Embodiments described herein are generally directed at vehicles thattransmit their behavior/location in the form of trajectory device to aserver, such as a location-based service provider. In the on-linescenario, the vehicle transmits the data in real-time such that thevehicle must decide when to start transmitting information. In thisscenario, the actual end of a trajectory cannot be known with certaintyin advance, even in the case of guided navigation as a vehicle may stopat a different location from where the navigator is aiming. This renderscropping of the end of the trajectories more difficult. In the off-linescenario, the vehicle transmits the trajectory data after the trajectoryis completed and the cropping of both the starting point (origin) andending point (destination) is done before transmission by the vehicle orassociated mobile device 114 or by the location-based service providerafter receiving the trajectory data.

The process of calculating uncertainty may be maintained for both thebeginning of a trajectory and the end of a trajectory. However, thetechniques described herein work backward, in reverse from the end of atrajectory to crop the last portion of the trajectory before thedestination. In a scenario in which the destination is known withcertainty (e.g., off-line scenario), the application of the processdescribed herein to the end of the trajectory is straight forward. Inboth scenarios, the algorithm understands the actual origin of thetrajectory such that the algorithm begins from there and processessequentially all points of the trajectory. In the on-line scenario,these points would arrive at the server in real-time as the vehicle'ssensors report movement of the vehicle, while in the off-line scenarioall points of the trajectory are saved in memory and can be accessedsynchronously.

According to an example embodiment described herein, the algorithmbegins at the actual origin of the trajectory and iterates on thesuccessive points in order. When a junction is encountered, a counter isupdated based on properties of the junction. The accessibility map isused to determine the properties of the junction and to identify thecontribution that junction makes toward anonymizing a trajectory. Thatcontribution is provided in a score with which the counter is updated.One such property of a junction is the number of alternative routesemanating from the junction. A more basic approach to incrementing thecounter would be to update the counter based on the number of road linksemanating from the junction without context. However, including context,such as population density, POI density, etc., can be used to moreaccurately determine where a trajectory should be cropped in order toanonymize the trajectory. Once the counter value is larger than apredetermined threshold value, the algorithm stops and crops thetrajectory data up to that point of the trajectory or beginstransmission of the trajectory in an on-line scenario. All data thatlies in the junction (e.g., the road link leading to the junction thatthe vehicle arrived at the junction on) may be cropped from thetrajectory data.

FIG. 3 illustrates an example embodiment of the cropping algorithm of anexample trajectory. In the illustrated example embodiment, the score foreach junction is based on the number of road links emanating from thejunction, with the road link used to enter the junction on thetrajectory subtracted from that number. As noted above, this is a basicexample of an implementation of the embodiments described herein. Thetrajectory starts along road link R1 that arrives at junction J1 andexits along road link R2. Here, Junction J1 is evaluated and the counterC is updated and incremented by the number of exits in junction J1, sothe counter is incremented to a value of two (C=2) including road linkR2 and alternate road link A1, but not including road link R1 as thatwas the road link along which the trajectory entered the junction. Thetrajectory continues along road link R2 to junction J2, where it exitsJ2 along road link R3. Counter C is incremented by the number of exitsin junction J2 or three (road link R3 and alternate segments A2 and A3)such that the counter reaches a total of five (C=5) upon the vehicleexiting junction J2 along road link R3. Five is less than a thresholdvalue of six, such that the trajectory through road link R3 remains aportion that will be cropped in an off-line scenario, or the vehicle maynot have begun transmitting a trajectory in an on-line scenario. Thevehicle reaches junction J3 along road link R3 and exits the junctionalong road link R4. As there are two exits available from junction J3(road link R4 and alternate road link A4) when arriving along road linkR3, the counter is incremented by two to reach a value of seven (C=7)such that the threshold of six is reached and exceeded. Thus, thetrajectory suitable for the location-based service provider begins atroad link R4. The portion of the trajectory including road links R1, R2,and R3 is cropped by deletion or removal of the portion of thetrajectory in an off-line scenario or beginning to transmit thetrajectory of the vehicle upon beginning to drive along road link R4 inan on-line scenario.

FIG. 4 illustrates an algorithm of an example embodiment for cropping atrajectory. A trajectory includes a plurality of probe data points,where the probe data points include at least location information andtimestamp information. The probe data points may be map-matched to roadlinks of a map to generate a trajectory including a plurality ofsequential road links in the map. Optionally, as in the algorithmdescribed below, the trajectory may not be identified as a sequence ofroad links and the probe data points may individually be map-matched toroad links as the algorithm loops through the analysis routine.

As shown in FIG. 4, given a trajectory T={p0, p1, p2, . . . pt}, wherepi is a probe data point, e.g., spatio-temporal coordinate including alocation and a timestamp. An index of the probe points “current_index”begins with a count of zero at step 2. The total count also begins atzero at step 3. The threshold is a number greater than two, but lessthan some predetermined maximum. The threshold may be determined atrandom from among a range of values to reduce the likelihood that atrajectory could be reverse-mapped to identify an origin or adestination as described further below.

The loop routine begins at step 5 and is performed until the total_countsatisfies the threshold. At step 5.a., the current index is incrementedby one as the loop routine “crawls” along the trajectory sequentially toeach probe data point. The current_point is set equal to the probe datapoint corresponding to the current index value (e.g., if current indexis 5, the probe data point p5 is the current_point). The current_segmentis a road link map-matched to the current_point. The road linkmap-matched to the current point is the road link along which thevehicle is determined to be or have been at the time the probe datapoint was generated. If the map-matched current_segment is the exit of ajunction (otherwise known as an intersection of three or more roadlinks), the total_count is incremented by a score, such as the number ofroad links that intersect at the junction, minus one to account for theroad link along which the vehicle entered the junction. As noted above,the score for a junction may be more complex and include additionalfactors, such as population density, POI density, or other properties ofthe accessibility map. The loop continues until the total_countsatisfies the threshold. Once the total_count satisfies the threshold,the trajectory T is set equal to the trajectory starting with thecurrent index or the next probe data point after the threshold wassatisfied. This “crops” the probe data points from the trajectory belowwhich the threshold was not satisfied.

While the above-described loop routine relies on map-matching a probedata point to a road link, map-matching may not be necessary. Asmap-matching can be processing intensive and be affected by a mapversion, embodiments described herein may associate a probe data pointto a map object or map element. A map element may include a geofencearound an area such as a junction or a road link, or a map element maybe a road link. Map-matching may require more rigid association of aprobe data point to a road link, while associating a probe data point toa map element may be less rigid and may provide more flexibility betweendiffering map versions or road links that do not identically alignbetween maps. Further, associating a probe data point to a map elementmay require less processing capacity than map-matching.

A higher threshold value results in a higher uncertainty about theactual origin of the trajectory as it increases the number ofalternative paths that the trajectory could have taken. The samealgorithm can be applied to the destination end of the trajectory bystarting from the end of the trajectory and processing the points inreverse order.

An adversary that aims to infer the actual origin of a croppedtrajectory could narrow down the possible alternative paths by reversingthe cropping algorithm. To do so, the adversary needs to know theproperties of the road network (e.g., the number of road links emanatingfrom or exiting a junction and the threshold used in cropping). FIG. 5illustrates a situation in which an adversary could narrow down theorigin of a cropped trajectory to only two road links. According to theillustrated embodiment, the threshold used has a value of three. Werethe original trajectory to start in either road link R4 or road link R6,the cropped trajectory would start in road link R5 or road link R7,respectively, as junction J3 and junction J4 have a number of exitsequal to the threshold. For this reason, an adversary can conclude thatthe origin of the trajectory must be road link R1 or road link R2.

Given that the properties of a road network are public information, anadversary must not know the threshold chosen by the algorithm.Embodiments described herein employ a threshold that is randomlyselected from a range of values. This range may be narrow while beingable to thwart adversaries from identifying origin road links.

The accessibility map data may include map data contained in mapdatabase 108 of the map developer 116 or a map service provider mayinclude links or segments, where each roadway in a mapped networkcomprises a series of interconnected links. Each link is associated withattributes about the geographical segment that they represent. A linkmay include link geometry data that is a list of coordinates thatrepresent the geographical entity. Links may also include a total lengthof the geographic segment they represent and travel heading/bearingalong the link. Further, information about the area around a road linkor junction may be included in the accessibility map, such as thepopulation density, POI density, etc.

Road links represented by links can be used in calculating a route orrecording a route as traveled. Nodes are end points corresponding to therespective links or segments of the road. Road link data records andnode data records may be stored, for example, in map database 108, andmay represent a road network. Road links and nodes can be associatedwith attributes such as geographic coordinates, street names, addressranges, speed limits, turn restrictions at intersections, and othernavigation related attributes, as well as points of interest (POIs),such as traffic controls (e.g., stoplights, stop signs, crossings,etc.), fuel stations, hotels, restaurants, museums, stadiums, offices,repair shops, buildings, stores, parks, etc. The map database 108 caninclude data about places, such as cities, towns, or other communities,and other geographic features, such as bodies of water, mountain ranges,etc. Such place or feature data can be part of POI data or can beassociated with POIs or POI data records.

The score of a junction may be based on the number of roads emanatingfrom the junction, and may also include a weighting factor orbonus/penalty for context of the junction. For example, a junction mayinclude four road links emanating from the junction. If the junction isin a heavily populated area, the junction is less likely to divulgeinformation about an individual, such that the score for the junctionmay be based on the number of road links emanating from the junction(e.g., four subtracting one for the path along which the junction wasentered) and a bonus weight or weight factor may be used to increase thescore of the junction. A junction in what is deemed a heavily populatedarea may be multiplied by a factor, such as 1.5 to increase the score ofthat junction, or the junction may be afforded a bonus, such as two, asthe junction is less likely to divulge private information, andcontributes more to the counter to reach the threshold beyond which thetrajectory may be used without being traceable to a unique individual.

Similarly, the score of a junction may include a penalty when thejunction is in a relatively remote location. A junction having four roadlinks emanating from the junction in a remote area may be weighted witha factor of 0.75, for example, to compensate for the junction notproviding substantial anonymity. Similarly, a penalty could be assessedto the junction, such that the number of road links emanating from thejunction may be reduced by two.

While junctions have been described above as having population-basedweighting factors, other context can also be implemented. For example, ajunction in a road may be a four-way intersection with four roadsemanating from the junction. However, two of those roads may be privateroads, dead end roads, or roads that otherwise discourage travel (e.g.,unpaved, narrow, low clearance, etc.). The context of the junction mayreflect this and may reduce the score of the junction as there istypically only one path through the intersection, avoiding theless-traveled roads that intersect there. Thus, the penalty to the scorecould be substantial and the junction could have a net score as littleas zero since it may provide no anonymity. Further, points-of-interestmay influence the penalty or bonus afforded to a junction, such as whenthe junction is proximate a hospital or rehabilitation center, forexample, which may be a particularly sensitive area for a user such thatjunctions proximate these types of POIs may be further penalized.

Beyond population-based weighting factors, junctions may have time-basedweighting factors and/or time-based and POI-type-based weightingfactors. For example, a junction proximate an office complex may be busyduring the day on weekdays, but relatively empty on weekends or atnight. This type of junction may therefore have a bonus-weighting duringthe day on weekdays as it can provide a greater degree of anonymity,while it may have a penalty-weighting at night or on weekends.Similarly, a stadium may have adjacent neighborhoods that haverelatively low traffic outside of events at the stadium. A scheduledevent at the stadium may weight junctions around the stadium differentlythan outside of scheduled events. These time epochs may influence theweighting of a junction in identifying the degree to which the junctionprovides anonymity. Optionally, a live traffic status may be used toweight a junction whereby the junction provides greater anonymity duringtimes of heavy traffic while the junction provides lesser anonymityduring times of low traffic.

While example embodiments above describe the cropping of a singletrajectory, example embodiments may be implemented on trajectories thatare segmented. For example, in an embodiment in which a trajectory issegmented into four trajectory portions, the first trajectory portionincludes the origin, and the fourth trajectory portion includes thedestination. The second and third trajectory portions are sufficientlyanonymized as they do not point to either an origin or a destination. Assuch, the cropping process may be implemented based on only the originand destination. For example, the first trajectory portion may becropped based on analysis of the trajectory starting with the origin.Similarly, the fourth trajectory portion may be cropped based onanalysis of the trajectory starting with the destination and workingbackwards. These trajectory portions combine to form a singletrajectory.

FIGS. 6 and 7 illustrate a flowcharts depicting methods according toexample embodiments of the present disclosure. It will be understoodthat each block of the flowcharts and combination of blocks in theflowcharts may be implemented by various means, such as hardware,firmware, processor, circuitry, and/or other communication devicesassociated with execution of software including one or more computerprogram instructions. For example, one or more of the proceduresdescribed above may be embodied by computer program instructions. Inthis regard, the computer program instructions which embody theprocedures described above may be stored by a memory device 204 of anapparatus employing an embodiment of the present invention and executedby a processor 202 of the apparatus. As will be appreciated, any suchcomputer program instructions may be loaded onto a computer or otherprogrammable apparatus (for example, hardware) to produce a machine,such that the resulting computer or other programmable apparatusimplements the functions specified in the flowchart blocks. Thesecomputer program instructions may also be stored in a computer-readablememory that may direct a computer or other programmable apparatus tofunction in a particular manner, such that the instructions stored inthe computer-readable memory produce an article of manufacture theexecution of which implements the function specified in the flowchartblocks. The computer program instructions may also be loaded onto acomputer or other programmable apparatus to cause a series of operationsto be performed on the computer or other programmable apparatus toproduce a computer-implemented process such that the instructions whichexecute on the computer or other programmable apparatus provideoperations for implementing the functions specified in the flowchartblocks.

Accordingly, blocks of the flowcharts support combinations of means forperforming the specified functions and combinations of operations forperforming the specified functions for performing the specifiedfunctions. It will also be understood that one or more blocks of theflowcharts, and combinations of blocks in the flowcharts, can beimplemented by special purpose hardware-based computer systems whichperform the specified functions, or combinations of special purposehardware and computer instructions.

FIG. 6 illustrates a method of anonymizing trajectories of mobiledevices, and more particularly, to pruning or cropping of a beginningand an end of a trajectory between an origin and a destination to removeidentifiable information from the trajectory. Probe data points defininga trajectory are received at 310. The probe data points may be receivedfrom a probe apparatus associated with a vehicle and including alocation and timestamp. For a subset of probe data points of thesequence of probe data points defining the trajectory, begin at theorigin with a counter set to zero at 320. Moving to a next probe datapoint, the counter value is updated at 330 based, at least in part, onthe number of road links emanating from each junction through which thetrajectory passed to reach a location associated with the respectiveprobe data point. At 340 it the counter is checked to see if the countersatisfies a predetermined threshold. The predetermined threshold may bea random value between 2 and an upper limit. If the counter does notsatisfy the threshold, the counter value is updated at the next probedata point at 330. If the counter satisfies the threshold at 340, probedata points from the trajectory preceding the probe data point thatcaused the counter to satisfy the predetermined threshold are removed toobtain origin-obscured probe data points at 350. A cropped trajectory iscreated at 360 including only the origin-obscured probe data points.

FIG. 7 illustrates another method of anonymizing trajectories of mobiledevices, and more particularly, to pruning or cropping of a beginningand an end of a trajectory between an origin and a destination to removeidentifiable information from the trajectory. Probe data points arereceived at 410 that include a location and timestamp. A trajectory isdetermined at 420 beginning at an origin and based on the probe data. Anext probe data point is map-matched to a road link at 430. A countervalue is updated at 440 at the next probe data point in response to thenext probe data point being map-matched to a road link exiting ajunction. At 450, the counter value is checked to determine if itsatisfies a predetermined threshold. If the counter value does notsatisfy the predetermined threshold, a next probe data point ismap-matched at 430. If the threshold is satisfied by the counter value,the trajectory is modified to being with the probe data point thatresulted in the counter value satisfying the threshold at 460.

In an example embodiment, an apparatus for performing the methods ofFIGS. 6 and 7 above may comprise a processor (e.g., the processor 202)configured to perform some or each of the operations (310-360 and410-460) described above. The processor may, for example, be configuredto perform the operations (310-360 and 410-460) by performing hardwareimplemented logical functions, executing stored instructions, orexecuting algorithms for performing each of the operations.Alternatively, the apparatus may comprise means for performing each ofthe operations described above. In this regard, according to an exampleembodiment, examples of means for performing operations 310-360 and410-460 may comprise, for example, the processor 202 and/or a device orcircuit for executing instructions or executing an algorithm forprocessing information as described above.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Moreover, although the foregoing descriptions and the associateddrawings describe example embodiments in the context of certain examplecombinations of elements and/or functions, it should be appreciated thatdifferent combinations of elements and/or functions may be provided byalternative embodiments without departing from the scope of the appendedclaims. In this regard, for example, different combinations of elementsand/or functions than those explicitly described above are alsocontemplated as may be set forth in some of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

That which is claimed:
 1. An apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to, with the processor, cause the apparatus to at least: receive probe data associated with a vehicle, wherein the probe data comprises probe data points, each probe data point including a location and a timestamp; determine a trajectory based on the probe data beginning at an origin; in response to a counter value failing to satisfy a predetermined value: advance to a next probe data point; associate the next probe data point to a map element; and in response to the map element corresponding to a junction, update the counter value based, at least in part, on a number of road links intersecting at the junction; in response to the counter value satisfying the predetermined value: modify the trajectory to begin with a probe data point associated with a map element corresponding to a junction having caused the counter to satisfy the predetermined value.
 2. The apparatus of claim 1, wherein the predetermined value comprises a random number within a predefined range.
 3. The apparatus of claim 1, further comprising causing the apparatus to remove from the trajectory any information identifying an entrance to a junction at a beginning of the modified trajectory.
 4. The apparatus of claim 1, wherein the apparatus is further caused to: estimate a destination of the trajectory; identify a boundary around the estimated destination of the trajectory; and end the modified trajectory at a last probe data point received outside of the boundary.
 5. The apparatus of claim 1, wherein causing the apparatus to provide the modified trajectory to a service provider comprises causing the apparatus to: provide the modified trajectory to a service provider with a time delay from the time at which the probe data was received; and cease to provide the modified trajectory in response to determining that the vehicle has reached a location proximate the destination.
 6. The apparatus of claim 1, wherein the number of road links intersecting at each junction is identified based on an accessibility map of a road network through which the trajectory passes.
 7. The apparatus of claim 6, wherein the accessibility map comprises information defining possible ways of entering and leaving junctions of the road network factoring in properties of the map including an allowable direction of travel in each road link.
 8. A computer program product comprising at least one non-transitory computer-readable storage medium having computer-executable program code portions stored therein, the computer-executable program code portions comprising program code instructions configured to: receive probe data associated with a vehicle, wherein the probe data comprises probe data points, each probe data point including a location and a timestamp; determine a trajectory based on the probe data beginning at an origin; in response to a counter value failing to satisfy a predetermined value: advance to a next probe data point; associate the next probe data point to a map element; and in response to the map element corresponding to a junction, update the counter value based, at least in part, on a number of road links intersecting at the junction; in response to the counter value satisfying the predetermined value: modify the trajectory to begin with a probe data point associated with a map element corresponding to a junction having caused the counter to satisfy the predetermined value.
 9. The computer program product of claim 8, wherein the predetermined value comprises a random number within a predefined range.
 10. The computer program product of claim 8, further comprising program code instructions to remove from the trajectory any information identifying an entrance to a junction at a beginning of the modified trajectory.
 11. The computer program product of claim 8, further comprising program code instructions to: estimate a destination of the trajectory; identify a boundary around the estimated destination of the trajectory; and end the modified trajectory at a last probe data point received outside of the boundary.
 12. The computer program product of claim 8, wherein the program code instructions to provide the modified trajectory to a service provider comprise program code instructions to: provide the modified trajectory to a service provider with a time delay from the time at which the probe data was received; and cease to provide the modified trajectory in response to determining that the vehicle has reached a location proximate the destination.
 13. The computer program product of claim 8, wherein the number of road links intersecting at each junction is identified based on an accessibility map of a road network through which the trajectory passes.
 14. The computer program product of claim 13, wherein the accessibility map comprises information defining possible ways of entering and leaving junctions of the road network factoring in properties of the map including an allowable direction of travel in each road link.
 15. A method comprising: receiving probe data associated with a vehicle, wherein the probe data comprises probe data points, each probe data point including a location and a timestamp; determining a trajectory based on the probe data beginning at an origin; in response to a counter value failing to satisfy a predetermined value: advancing to a next probe data point; associating the next probe data point to a map element; and in response to the map element corresponding to a junction, updating the counter value based, at least in part, on a number of road links intersecting at the junction; in response to the counter value satisfying the predetermined value: modifying the trajectory to begin with a probe data point associated with a map element corresponding to a junction having caused the counter to satisfy the predetermined value.
 16. The method of claim 15, wherein the predetermined value comprises a random number within a predefined range.
 17. The method of claim 15, further comprising removing from the trajectory any information identifying an entrance to a junction at a beginning of the modified trajectory.
 18. The method of claim 15, further comprising: estimating a destination of the trajectory; identifying a boundary around the estimated destination of the trajectory; and ending the modified trajectory at a last probe data point received outside of the boundary.
 19. The method of claim 15, wherein providing the modified trajectory to a service provider comprises: providing the modified trajectory to a service provider with a time delay from the time at which the probe data was received; and ceasing to provide the modified trajectory in response to determining that the vehicle has reached a location proximate the destination.
 20. The method of claim 15, wherein the number of road links intersecting at each junction is identified based on an accessibility map of a road network through which the trajectory passes. 